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Showing papers by "Anthony G. A. Brown published in 2016"


Journal ArticleDOI
TL;DR: Gaia as discussed by the authors is a cornerstone mission in the science programme of the European Space Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach.
Abstract: Gaia is a cornerstone mission in the science programme of the EuropeanSpace Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page.

5,164 citations


Journal ArticleDOI
TL;DR: The first Gaia data release, Gaia DR1 as discussed by the authors, consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues.
Abstract: Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. Aims: A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Methods: The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue. Results: Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues - a realisation of the Tycho-Gaia Astrometric Solution (TGAS) - and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of 3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr-1 for the proper motions. A systematic component of 0.3 mas should be added to the parallax uncertainties. For the subset of 94 000 Hipparcos stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr-1. For the secondary astrometric data set, the typical uncertainty of the positions is 10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to0.03 mag over the magnitude range 5 to 20.7. Conclusions: Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data.

2,174 citations


Journal ArticleDOI
C. Fabricius1, Ulrich Bastian2, Jordi Portell1, J. Castañeda1, Michael Davidson3, Nigel Hambly3, M. Clotet1, M. Biermann2, A. Mora, Deborah Busonero, Alberto Riva, Anthony G. A. Brown4, Richard L. Smart, Uwe Lammers5, J. Torra1, R. Drimmel, G. Gracia, W. Löffler2, A. Spagna, Lennart Lindegren6, Sergei A. Klioner7, Alexandre Humberto Andrei, N. Bach, L. Bramante8, T. Brüsemeister2, G. Busso4, G. Busso9, J. M. Carrasco1, Mario Gai, N. Garralda1, J. J. González-Vidal1, Raphael Guerra5, M. Hauser2, Stefan Jordan2, Carme Jordi1, H. Lenhardt2, Francois Mignard, R. Messineo8, A. F. Mulone8, I. Serraller1, U. Stampa2, Paolo Tanga, A. van Elteren4, W. van Reeven, Holger Voss1, Ummi Abbas, Walter Allasia, Martin Altmann2, Martin Altmann10, S. Anton11, Christophe Barache10, Ugo Becciani12, Jérôme Berthier13, Luciana Bianchi, Alex Bombrun, S. Bouquillon10, G Bourda14, B. Bucciarelli, A. G. Butkevich7, R. Buzzi, Rossella Cancelliere, T. Carlucci10, Patrick Charlot14, Ross Collins3, G. Comoretto15, Nicholas Cross3, Mariateresa Crosta, F. de Felice16, Agnes Fienga, Francesca Figueras1, E. Fraile, R. Geyer7, Jose M Hernandez5, David Hobbs6, W. Hofmann2, Shilong Liao17, E. Licata, M. Martino8, Paul J. McMillan6, Daniel Michalik6, R. Morbidelli, P. Parsons, M. Pecoraro, M. Ramos-Lerate, M. Sarasso, H. I. Siddiqui15, Iain A. Steele18, H. Steidelmüller7, F. Taris10, Alberto Vecchiato, A. Abreu15, E. Anglada19, Steve Boudreault20, Steve Boudreault21, Mark Cropper20, B. Holl, N. Cheek19, C. Crowley, J. M. Fleitas, A. Hutton, J. Osinde, Nicholas Rowell3, E. Salguero, E. Utrilla, Nadejda Blagorodnova1, Nadejda Blagorodnova22, Michael Soffel7, J. Osorio11, D. Vicente23, J. Cambras, H.-H. Bernstein2 
TL;DR: The first data release from the Gaia mission contains accurate positions and magnitudes for more than a billion sources, and proper motions and parallaxes for the majority of the 2.5 million HIPPARCOS and Tycho-2 stars as mentioned in this paper.
Abstract: Context. The first data release from the Gaia mission contains accurate positions and magnitudes for more than a billion sources, and proper motions and parallaxes for the majority of the 2.5 million HIPPARCOS and Tycho-2 stars. Aims. We describe three essential elements of the initial data treatment leading to this catalogue: the image analysis, the construction of a source list, and the near real-time monitoring of the payload health. We also discuss some weak points that set limitations for the attainable precision at the present stage of the mission. Methods. Image parameters for point sources are derived from one-dimensional scans, using a maximum likelihood method, under the assumption of a line spread function constant in time, and a complete modelling of bias and background. These conditions are, however, not completely fulfilled. The Gaia source list is built starting from a large ground-based catalogue, but even so a significant number of new entries have been added, and a large number have been removed. The autonomous onboard star image detection will pick up many spurious images, especially around bright sources, and such unwanted detections must be identified. Another key step of the source list creation consists in arranging the more than 10^(10) individual detections in spatially isolated groups that can be analysed individually. Results. Complete software systems have been built for the Gaia initial data treatment, that manage approximately 50 million focal plane transits daily, giving transit times and fluxes for 500 million individual CCD images to the astrometric and photometric processing chains. The software also carries out a successful and detailed daily monitoring of Gaia health.

108 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the calibration model of the Gaia photometric passband for Gaia Data Release 1, focussing on the G band photometry, and describe the photometric calibration pipeline explained here was applied to the first data release with good results.
Abstract: Context. Gaia is an ESA cornerstone mission launched on 19 December 2013 aiming to obtain the most complete and precise 3D map of our Galaxy by observing more than one billion sources. This paper is part of a series of documents explaining the data processing and its results for Gaia Data Release 1, focussing on the G band photometry. Aims. This paper describes the calibration model of the Gaia photometric passband for Gaia Data Release 1. Methods. The overall principle of splitting the process into internal and external calibrations is outlined. In the internal calibration, a self-consistent photometric system is generated. Then, the external calibration provides the link to the absolute photometric flux scales. Results. The Gaia photometric calibration pipeline explained here was applied to the first data release with good results. Details are given of the various calibration elements including the mathematical formulation of the models used and of the extraction and preparation of the required input parameters (e.g. colour terms). The external calibration in this first release provides the absolute zero point and photometric transformations from the Gaia G passband to other common photometric systems.Conclusions. This paper describes the photometric calibration implemented for the first Gaia data release and the instrumental effects taken into account. For this first release no aperture losses, radiation damage, and other second-order effects have not yet been implemented in the calibration.

93 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of the photometric data that are part of the first Gaia data release, and the overall precision for the Gaia photometry is shown to be at the milli-magnitude level and has a clear potential to improve further in future releases.
Abstract: Context. This paper presents an overview of the photometric data that are part of the first Gaia data release. Aims. The principles of the processing and the main characteristics of the Gaia photometric data are presented. Methods. The calibration strategy is outlined briefly and the main properties of the resulting photometry are presented. Results. Relations with other broadband photometric systems are provided. The overall precision for the Gaia photometry is shown to be at the milli-magnitude level and has a clear potential to improve further in future releases.

67 citations


Journal ArticleDOI
TL;DR: In this article, the authors used self-consistent numerical simulations of the evolution and disruption of the Sun's birth cluster in the Milky Way potential to investigate the present-day phase space distribution of the sun's siblings.
Abstract: We use self-consistent numerical simulations of the evolution and disruption of the Sun's birth cluster in the Milky Way potential to investigate the present-day phase space distribution of the Sun's siblings. The simulations include the gravitational N-body forces within the cluster and the effects of stellar evolution on the cluster population. In addition the gravitational forces due to the Milky Way potential are accounted for in a self-consistent manner. Our aim is to understand how the astrometric and radial velocity data from the Gaia mission can be used to pre-select solar sibling candidates. We vary the initial conditions of the Sun's birth cluster, as well as the parameters of the Galactic potential. We show that the disruption time-scales of the cluster are insensitive to the details of the non-axisymmetric components of the Milky Way model and we make predictions, averaged over the different simulated possibilities, about the number of solar siblings that should appear in surveys such as Gaia or GALAH. We find a large variety of present-day phase space distributions of solar siblings, which depend on the cluster initial conditions and the Milky Way model parameters. We show that nevertheless robust predictions can be made about the location of the solar siblings in the space of parallaxes ($\varpi$), proper motions ($\mu$) and radial velocities ($V_\mathrm{r}$). By calculating the ratio of the number of simulated solar siblings to that of the number of stars in a model Galactic disk, we find that this ratio is above 0.5 in the region given by: $\varpi \geq 5$mas, $4 \leq \mu \leq 6$masyr$^{-1}$, and $-2\leq V_\mathrm{r} \leq 0$kms$^{-1}$. Selecting stars from this region should increase the probability of success in identifying solar siblings through follow up observations [Abridged].

44 citations


Journal ArticleDOI
TL;DR: The European Space Agency's Gaia satellite was launched into orbit around L2 in December 2013 with a payload containing 106 large-format scientific CCDs, which are continuously operated in a mode where the line clock rate and the satellite rotation spin-rate are in synchronisation as mentioned in this paper.
Abstract: The European Space Agency’s Gaia satellite was launched into orbit around L2 in December 2013 with a payload containing 106 large-format scientific CCDs. The primary goal of the mission is to repeatedly obtain high-precision astrometric and photometric measurements of one thousand million stars over the course of five years. The scientific value of the down-linked data, and the operation of the onboard autonomous detection chain, relies on the high performance of the detectors. As Gaia slowly rotates and scans the sky, the CCDs are continuously operated in a mode where the line clock rate and the satellite rotation spin-rate are in synchronisation. Nominal mission operations began in July 2014 and the first data release is being prepared for release at the end of Summer 2016. In this paper we present an overview of the focal plane, the detector system, and strategies for on-orbit performance monitoring of the system. This is followed by a presentation of the performance results based on analysis of data acquired during a two-year window beginning at payload switch-on. Results for parameters such as readout noise and electronic offset behaviour are presented and we pay particular attention to the effects of the L2 radiation environment on the devices. The radiation-induced degradation in the charge transfer efficiency (CTE) in the (parallel) scan direction is clearly diagnosed; however, an extrapolation shows that charge transfer inefficiency (CTI) effects at end of mission will be approximately an order of magnitude less than predicted pre-flight. It is shown that the CTI in the serial register (horizontal direction) is still dominated by the traps inherent to the manufacturing process and that the radiation-induced degradation so far is only a few per cent. We also present results on the tracking of ionising radiation damage and hot pixel evolution. Finally, we summarise some of the detector effects discovered on-orbit which are still being investigated.

41 citations


Journal ArticleDOI
TL;DR: The European Space Agency's Gaia satellite was launched into orbit around L2 in December 2013 with a payload containing 106 large-format scientific CCDs as mentioned in this paper, and the primary goal of the mission is to repeatedly obtain high-precision astrometric and photometric measurements of one thousand million stars over the course of five years.
Abstract: The European Space Agency's Gaia satellite was launched into orbit around L2 in December 2013 with a payload containing 106 large-format scientific CCDs. The primary goal of the mission is to repeatedly obtain high-precision astrometric and photometric measurements of one thousand million stars over the course of five years. The scientific value of the down-linked data, and the operation of the onboard autonomous detection chain, relies on the high performance of the detectors. As Gaia slowly rotates and scans the sky, the CCDs are continuously operated in a mode where the line clock rate and the satellite rotation spin-rate are in synchronisation. Nominal mission operations began in July 2014 and the first data release is being prepared for release at the end of Summer 2016. In this paper we present an overview of the focal plane, the detector system, and strategies for on-orbit performance monitoring of the system. This is followed by a presentation of the performance results based on analysis of data acquired during a two-year window beginning at payload switch-on. Results for parameters such as readout noise and electronic offset behaviour are presented and we pay particular attention to the effects of the L2 radiation environment on the devices. The radiation-induced degradation in the charge transfer efficiency (CTE) in the (parallel) scan direction is clearly diagnosed; however, an extrapolation shows that charge transfer inefficiency (CTI) effects at end of mission will be approximately an order of magnitude less than predicted pre-flight. It is shown that the CTI in the serial register (horizontal direction) is still dominated by the traps inherent to the manufacturing process and that the radiation-induced degradation so far is only a few per cent. Finally, we summarise some of the detector effects discovered on-orbit which are still being investigated.

33 citations


Posted Content
TL;DR: The Gaia archive is being designed and implemented by the DPAC Consortium as mentioned in this paper, and the purpose of the archive is to maximize the scientific exploitation of the Gaia data by the astronomical community.
Abstract: The Gaia archive is being designed and implemented by the DPAC Consortium The purpose of the archive is to maximize the scientific exploitation of the Gaia data by the astronomical community Thus, it is crucial to gather and discuss with the community the features of the Gaia archive as much as possible It is especially important from the point of view of the GENIUS project to gather the feedback and potential use cases for the archive This paper presents very briefly the general ideas behind the Gaia archive and presents which tools are already provided to the community

1 citations


Proceedings ArticleDOI
TL;DR: The Gaia Data Processing and Analysis Consortium (DPAC) as discussed by the authors is a large, multi-national, science consortium which has to handle and process the dense and complex Gaia data stream.
Abstract: With its launch at the very end of 2013, ESA's astrometry satellite Gaia began its endeavor to compile astrometric and photometric measurements of at least one billion objects, as well as high resolution optical spectra of hundred million objects. The Gaia catalog therefore results in a wealth of coherently determined astrophysical parameters of these objects. After its extensive commissioning phase, Gaia entered the nominal mission phase in July 2014. The science ground segment, which is formed by the Gaia Data Processing and Analysis Consortium (DPAC), has since then started its operations. DPAC is a large, multi-national, science consortium which has to handle and process the dense and complex Gaia data stream. With its decentralized management and its distributed infrastructure, the Gaia DPAC is a remarkable undertaking. In this paper we will summarize some of the experiences of the DPAC facing the real Gaia data, compare this to the pre-launch expectations, and critically review the development phase.